Vehicle wheels are the part of a vehicle in contact with a driving surface, such as a road, and bear the entire weight of the vehicle during its operation. As such, it is important to monitor wheel condition, for example wheel alignment, wheel suspension and tire inflation, to determine whether maintenance needs to be performed to ensure optimal performance and safety of the vehicle.
The prior art is replete with systems for performing wheel alignment assessment. Most of these systems require equipment mounted on the wheels to assist in wheel alignment assessment and require the vehicle to be hoisted on to or otherwise mounted on to rollers or other apparatuses. A number of non-contact or contactless systems have been developed that employ optical measuring means, for example United States patents and Published Patent Applications: U.S. Pat. No. 6,545,750; U.S. Pat. No. 5,532,816; U.S. Pat. No. 4,899,218; U.S. Pat. No. 5,818,574; U.S. Pat. No. 6,400,451; U.S. Pat. No. 4,863,266; U.S. Pat. No. 7,336,350; U.S. Pat. No. 8,107,062; U.S. Pat. No. 7,864,309; U.S. Pat. No. 7,177,740; U.S. Pat. No. 6,657,711; U.S. Pat. No. 5,978,077; U.S. Pat. No. 7,454,841; U.S. Pat. No. 7,774,946; and US 2006/0152711, the entire contents of all of which are herein incorporated by reference. These systems involve laser displacement sensors, laser illumination, cameras or some combination thereof. Most of them require the vehicle to be stationary while the system operates. Some involve rotation of the wheels. Various parts of the wheel, including the tire sidewalls, can be used as targets for the lasers and/or cameras.
In one example, U.S. Pat. No. 5,532,816 discloses a contactless system for determining vehicle wheel alignment in which a point on a rotating wheel is tracked by a laser tracking unit to generate a signal directly representative of the rotational plane of the wheel. This signal is compared to a mathematically stored model to determine wheel alignment conditions. Both the vehicle and laser tracking unit are translationally stationary with respect to each other. The actual laser rotates to be able to follow the point on the rotating wheel.
In U.S. Pat. No. 5,532,816 the vehicle is mounted on rollers to allow the wheels to turn while the vehicle itself does not move. It would be advantageous to have a system that could make wheel alignment assessments while the vehicle itself is moving, for example while it is being driven into a garage or test station. Only a very few prior art systems are configured to permit wheel alignment assessment while the vehicle itself is moving.
U.S. Pat. No. 6,545,750 discloses a system for determining the dynamic orientation of a vehicle wheel plane. The system involves an orientation determining device that is not mounted on the vehicle or vehicle wheels. The orientation determining device remains stationary as a vehicle is driven by it and the device takes measurements on the wheel as the wheel passes by. The wheel is preferably outfitted with a reflective test surface. The orientation determining device comprises three transducers that emit beams of e/m radiation (e.g. lasers). The beams reflect off the test surface (or wheel hub) at three non-collinear points and the distance information from the three points is used to calculate wheel orientation at one specific instance in time. This system uses distance information from three separate laser beams to measure the distance to three different points on the wheel at a single instance in time. However, because the system is making measurements at only a single instance in time, it provides data only on wheel alignment, not on other wheel conditions such as wheel suspension and/or tire inflation. Further, acquiring data simultaneously on three non-collinear points on a wheel hub is difficult, so a reflective test surface is preferably mounted on the wheel, making the system more laborious and less useful for “on the go” wheel alignment assessment.
There remains a need for a simple method and apparatus for assessing the condition of a wheel on a vehicle while the vehicle is being driven and without the need to mount any equipment on the vehicle.